1. Field of the Invention
The present invention generally relates to wellbore completion. More particularly, the invention relates to an apparatus and method for expanding a tubular body. More particularly still, the invention relates to an expander tool for expanding a section of tubulars within a wellbore.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a string of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using methods known in the art, the casing is cemented into the wellbore by circulating cement into an annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of a formation surrounding the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth and a second string of smaller diameter casing or liner is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second casing string is then fixed or “hung” off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever decreasing diameter.
Apparatus and methods are emerging that permit tubular bodies to be expanded within a wellbore. Using this technology, a tubular string can be hung off a prior string by expanding its diameter in an area of overlap with the prior string. Further, an entire string of casing could be expanded to create a “monobore” diameter of casing in a well. The apparatus typically includes an expander tool that is run into the wellbore on a working string. The expander tool includes radially expandable members, or “expansion assemblies,” which are urged radially outward from a body of the expander tool, either in response to mechanical forces, or in response to fluid pressure in the working string. The expansion assemblies are expanded into contact with a surrounding tubular body. Outward force applied by the expansion assemblies cause the surrounding tubular to be expanded. Rotation of the expander tool, in turn, creates a circumferential expansion of the tubular. An exemplary rotary expander tool is described in U.S. Pat. No. 6,457,532 issued to Simpson on Oct. 1, 2002, which is herein incorporated by reference in its entirety.
Another example of an exemplary expansion tool is illustrated in FIGS. 1 and 2. More specifically, FIG. 1 is an exploded view of an exemplary expander tool 100. FIG. 2 presents the same expander tool 100 in cross-section, with the view taken across line 2-2 of FIG. 1.
The expander tool 100 has a body 102 which is hollow and generally tubular. The central body 102 has a plurality of recesses 114 to hold a respective expansion assembly 110. Each of the recesses 114 has substantially parallel sides and holds a respective piston 120. The pistons 120 are radially slidable, one piston 120 being slidably sealed within each recess 114. The back side of each piston 120 is exposed to the pressure of fluid within a hollow bore 115 of the expander tool 100. In this manner, pressurized fluid provided from the surface of the well can act upon the pistons 120 and cause them to extend outwardly.
Disposed above each piston 120 is a roller 116. The rollers 116 are near cylindrical and slightly barrel shaped. Each of the rollers 116 is supported by a shaft 118 at each end of the respective roller 116 for rotation about a respective axis. The rollers 116 are generally parallel to the longitudinal axis of the tool 100. In the arrangement of FIG. 1, the plurality of rollers 116 is radially offset at mutual 120-degree circumferential separations around the central body 102. In the arrangement shown in FIG. 1, two offset rows of rollers 116 are shown. However, only one row or more than two rows of roller 116, may be incorporated into the body 102.
As sufficient pressure is generated on the bottom piston surface behind the expansion assembly 110, the tubular being acted upon (not shown) by the expander tool 100 is expanded past a point of elastic deformation. In this manner, the diameter of the tubular is increased within the wellbore. By rotating the expander tool 100 in the wellbore and/or moving the expander tool 100 axially in the wellbore with the expansion assemblies 110 actuated, a tubular can be expanded into plastic deformation along a predetermined length.
Even though the known expander tools, such as the tool 100 shown in FIGS. 1-2, may be used to expand a surrounding tubular, they are not always reliable. For example, the rollers 116 in the known expander tools may overheat at their back face as the expander tool is urged axially through a tubular due to friction between the rotating rollers 116 and the stationary thrust bearing which leads to premature wear and subsequently to premature failure of the expander tool. In another example, an outer surface of the rollers 116 in the known expander tools may be subject to a differential speed at one end of the roller 116 relative to the other end of the roller 116 while expanding the surrounding tubular, which results in a residual torsional effect in the tubular and other inefficiencies, such as wear, heat, and increased torque. The differential speed is due to the varying diameter of the tubular as it is being expanded by contact with the roller 116 that also has a varying diameter. In a further example, the expansion assembly 110 in the known expander tools may misalign with the centerline of the tool 100 while expanding the surrounding tubular, which may result in a premature failure of the tool 100. As the tool 100 moves through a tubular, uneven radial force between the first and second ends of the roller cause the misalignment. In yet another example, the known expander tools, such as the tool 100 shown in FIGS. 1-2, may lack a sufficient maximum expansion ratio and may provide limited size of the thrust bearing due to dimensional constraints.
Therefore, a need exists for an improved expander tool that will address the above mentioned problems.